In situ X-ray diffraction evidence of field-induced transitions in a PbHfO3 single crystal

Antiferroelectric (AFE) materials are interesting due to recent discoveries of new prospective applications, although the mechanisms of the phase transitions that are at the heart of these applications remain incompletely understood. This work is devoted to the study of a single crystal of a model AFE, lead hafnate, by X-ray diffraction with in situ application of an electric field to trigger the transition to a polar phase. Two consecutive experiments were carried out on a 35 µm thick plate with [110] surface normal orientation over a field range from 0 to 330 kV cm⁻¹ and back. A sharp drop in the intensity of R- and Σ-type reflections around 225 kV cm⁻¹ was registered, with almost complete disappearance after 250 kV cm⁻¹. This is compatible with a field-induced phase transition from the AFE to the R3m polar phase, which was suggested earlier on the basis of non-diffraction characterizations. X-ray diffraction reveals that the AFE domains with displacements parallel to the field direction react much more smoothly to the field, gradually reducing the AFE order at very small fields instead of holding it almost constant up to the critical field value, which is naturally expected. This expectation is fulfilled for domains with other orientations, but only for the first switching cycle; in the second switching cycle the AFE order already shows a notable decrease at subcritical fields. It is suggested that these observations could be linked with the antiphase domain wall population being affected by the field, which is consistent with the observation of diffuse rods between the Γ and Σ points. Another remarkable observation is the much smoother recovery of the AFE phase compared with its sharp disappearance at the critical field.